The present invention relates generally to the field of coal pulverizers and, in particular, to a new and useful housing liner for an EL type or other pulverizer. More particularly, the present invention is drawn to a feature for the housing liner which provides for longer wear life and reduced incidences of parts failures.
Coal pulverizers are used to grind, dry and classify raw chunks of coal into fine solids which can be fluidized and fed, for example, to burners used in conjunction with industrial or utility boilers or furnaces. See, for example, U.S. Pat. Nos. 2,275,595 and 2,378,681. As is known to those skilled in the art, several different types of coal pulverizers, or coal mills, exist today, including one known by the designation xe2x80x9cEL.xe2x80x9d
EL type pulverizers were first produced in the early 1950""s. EL type pulverizers are ball-and-ring (or ball-and-race) type pulverizers which employ the ball-bearing principle to grind the coal. This design uses two vertical axis horizontal grinding rings, and a set of balls is placed between the grinding rings. The lower or bottom grinding ring rotates through connection to a rotating, vertical main shaft, while the upper or top grinding ring remains stationary and is spring loaded to create grinding pressure.
The coal is ground by contact with the upper and lower grinding rings and balls (collectively, the grinding elements). The lower and upper grinding rings are each provided with a race having a predefined, matching track contour that engages the balls. The force from the upper grinding ring pushes the balls against the coal layer on the lower grinding ring. The grinding rings and the balls are made of abrasion resistant alloys and comprise the major wear parts of the mill. Ground coal is swept from the grinding zone defined by the grinding rings and the balls by air for final particle size classification and subsequent pneumatic transport to one or more coal burners.
For further details of such EL type pulverizers, see Chapter 12 of Steam/Its Generation and Use, 40th Edition, Stultz and Kitto, Eds., Copyright (copyright)1992, The Babcock and Wilcox Company, the text of which is hereby incorporated by reference as though fully set forth herein.
Existing EL pulverizers include a housing unit made up of a plurality of circumferentially extending, side-by-side, replaceable housing liners. Known housing liners have one or no flutes as illustrated in FIG. 1. Housing liner 10 has an inner curved surface 12 that faces the balls. A single flute 14 that is inclined with respect to the vertical axis of the pulverizer is fixed to the inner surface. With the one-flute or no-flute design, excessive erosion is experienced with erosive coals. Efforts to stop or reduce this erosion have not been successful to date.
FIG. 3 shows the single fluted housing liner 10 after a period of use, with an area 18 that has been completely eroded through the liner on one side of the flute 14 and the flute itself greatly eroded. This is an extremely dangerous condition since it only leaves the relatively thin housing wall as the only shield between the pulverized coal and workers in the area of the pulverizer.
It is an object of the present invention to provide a pulverizer housing liner comprising an arcuate liner body having an inner curved surface forming a segment of a circular housing unit and two circumferentially spaced flutes fixed to the inner surface.
A further object of the invention is to provide the flutes at a spacing that reduces recirculation or impact zones ahead of or behind adjacent flutes in the particular liner in question, and in upstream or downstream lines around the housing unit.
The advantages of the invention are thus in the prevention of coal recirculation or impact zones ahead or behind adjacent flutes. The added flute material also acts as a sacrificial wear surface. For equivalent wear periods with the same coal, erosion of the liner is significantly reduced as illustrated by comparing FIGS. 3 and 4. The exterior of the housing is thus better protected against premature wear through. Premature wear through of the exterior housing is a hazard to life and property as large quantities of combustible coal could be released from the pulverizer due to premature housing liner wear.
Accordingly, another object of the invention is to provide the housing liner with a plurality of flutes, including more than two flutes in pulverizers with higher processing rates or sizes or pulverizers with circumferentially longer housing liners.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.